As discussed in U.S. Pat. No. 5,547,589, in conventional sanitation systems using a septic tank, waste water from a home empties into the septic tank, solids accumulate and decompose on the bottom of the tank and an effluent flows from the top of the tank into a drain field. The drain field, located a few feet below ground level, is intended to diffuse the effluent into the soil, where suspended solids are filtered out and natural bacterial matter in the soils consumes the solids and other organisms as the effluent slowly leaches through the soil eventually reaching the ground water in a purified state. The typical drain field comprises of an effluent dispersal system of inclined conduits with holes at the bottom facing a stone bed, the stone providing a flow path to the surrounding soil from the holes and preventing the soil from filling the holes.
But drainfields can become contaminated over time. Even new drain fields can exhibit the problems of contaminated fields if the water table is too high, or the soil is too compacted or otherwise has poor filtering and leaching qualities. In fact, the reality is that a drain field begins to deteriorate from the moment it is covered up. After that, proper performance is "assumed", but many factors not only shorten the useful life of drain field but reduce its ability to purify the effluent. The soil characteristics can change or might not be consistent. The water table may rise. Roots from trees interfere with the leaching action. Substances in the effluent can interfere with bacterial action in the soil and speed the growth to the biomat that eventually seals off the top of the field. (Biomat is the slimy biological material that accumulates at the soil interface.)
For the homeowner, the essential problem, when a drain field is contaminated, is that the effluent is not absorbed and backs up to the septic tank. For the environment, it means that the effluent is not being cleansed completely. When a drain field is clogged, the repair is drastic, complicated and expensive. The entire field must be dug up and a new trench of several hundred square feet minimum made. Often, trees and shrubbery have to removed. Drainfield repair assumes that there is adequate land to install a new drain field and that soil qualities provide adequate absorption. Smaller plots can make it extremely difficult to layout drainfields, with the separation to ground water mandated by local ordinances. If the ground water level is too high or the soil qualities are poor, the leach field may have to be elevated when a system is repaired or, in a new home, large volumes of top soil will be needed to achieve required ground water separation and drain field elevations.
Topographical conditions and new, more stringent governmental regulations can make it impossible to install an effective new drain field. Septic systems are used only where building plots are relatively large; that is, there is enough square footage to have the required drain field area for the expected effluent outflow from the home and maintain proper spacing between the drain field and a domestic water well. The alternative sewer systems are expensive to install and, generally speaking, do not return water in the effluent back to the surrounding environment. In any case, many suburban communities have no access to sewer systems. From an environment perspective a septic system makes sense, because water consumed by a household is recycled. A typical home can consume a considerable amount of water each day, all of it ultimately entering the drainfield, where most of it ideally eventually enters the water table, far below, filtered by the soil as it leaches down.